1. Field of the Invention
The present invention relates to a sample-and-hold circuit including an operational amplifier as an input circuit.
2. Related Art
A conventional sample-and-hold circuit has an operational amplifier, an analog switch and a charge storage capacitor which holds a potential charge therein. However, when the conventional sample-and-hold circuit is built in a monolithic integrated circuit (IC), a BiCMOS process, which will increase the cost of IC production, is needed because the operational amplifier is made of bipolar transistors and the analog switch is made of a MOSFET. An operational amplifier is known in which output transistors forming a push-pull circuit are cut off in response to a control signal. However, if an input signal drastically changes while the output signal is held, an AC coupling may occur at a phase compensation capacitor disposed in the operational amplifier. This causes the AC coupled signal to be transferred to the push-pull circuit. Thus, the potential of a charge storage capacitor to which the operational amplifier is connected may change, and the output signal may also change.